Its properties, like other crystalline materials, depend on how its atoms sit within the crystal lattice. Normally, silicon atoms form a diamond cubic crystal structure. However, if they can be forced to take up different arrangements they may impart new, and useful properties to the silicon.
Prof. Andrei Rode, Prof. Jim Williams, A/Prof. Jodie Bradby, and colleagues at the Australian National University (ANU) and University College London have used electron microscopy and computer modeling to predict potential alternative structures for silicon. They already knew that ordinary materials can adopt new and unusual crystal structures when exposed to extraordinarily high pressure and temperature. By using ultrashort (100 quadrillionths of a second) laser pulses they induced microexplosions inside the silicon to create extremely high pressures, and temperatures. This process effectively creates a contained plasma that then cools incredibly quickly, so new atomic arrangements form energetically stable structures.
In the AMMRF (now Microscopy Australia) at ANU the researchers used a combination of advanced electron microscopy techniques to visualise and measure the new crystalline structures with electron diffraction. They identified two of the computer-predicted structures, neither of which had been previously experimentally reported. Several additional structures were also observed that are now being studied in more detail. The computer predictions suggest that the new structures could have semiconducting to semi-metallic and possibly superconducting properties.
These findings and methods are helping pave the way for exciting new materials to be developed.
Rapp et al. Nat. Commun., 6, Article number: 7555, 2015 DOI: 10.1038/ncomms8555